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FX Maverick Tuning Help

Well I turned HST in all the way. I hit max velocity at about 1/2 turn ccw, 979fps. 34gr pellets. The power wheel had only slight effect on velocity. I then tried to set things for 26 gr pellets. Front 100 back 70. HST again around 1/2 turn ccw. Velocity was all over the place. I am surprised that the HST is so close to minimum. I remain a bit confused. I wonder if it has the stock hammer or something else.
 
I would suggest pulling the hammer to see what you have. This could definitely contribute to your issue. I've played with different hammers and while there is some overlap, they mostly serve a specific caliber/weight/pressure combo. So if you have the "wrong" hammer, you may never find your tune.

Also, tuning is a process of working the pressure and hammer tension up until you achieve your desired speed/consistency. You may benefit to start well below your target pressure. Find the max hammer tension for that pressure. Then bump up the pressure and hammer tension in unison until you get really close to your goal. Then some fine tuning to lock it in. (Don't mean to tell you what you already know...)

100/70 seems low pressure for the 26gr pellets (but I haven't tuned for them). I'd guess somewhere between 80 and 100 on the low pressure regulator would be better. My guess is the pressure is so low, that even with little hammer tension you are slapping the regulator very hard. This would overpower the pressure behind the regulator and could lead to inconsistent valve float. You may also be keeping the regulator open too long leading to extra air after the shot has left the barrel.
 
I purchased my .30 Maverick Sniper new. It came from FX with a 11 gram hammer weight and short hammer spring. I was not able to get anywhere near the advertised FPE after hours and hours of tuning and trying to figure it out. What I finally determined was the gun was shipped with the wrong hammer weight for .30 caliber.
I switched to a 13 gram hammer weight and it made a huge difference and I can easily tune the gun to over 100 FPE and still have the short spring in it.

I guess what I am trying to say is RegCreep makes a good point about the hammer weights.